There has been a long recognized need for a cosmetic or medicinal vehicle which is highly substantive, i.e., highly resistant to removal by water. Such a vehicle would be of particular interest in a sunscreen composition for use by bathers or any other person whose occupation or life-style made it necessary to be exposed to the actinic rays of the sun.
Many of the sunscreen compositions which have been known heretofore have been easily removed by water. Thus, repeated applications of the product become necessary for persons who swim, remain in the water outdoors for extended periods, or perspire freely.
The vehicles of this invention are also useful in medicinal emulsions for the topical application of certain dermatologically compatible medicaments, particularly anti-inflammatory steroids, e.g. betamethasone valerate and betamethasone dipropionate. These medicaments find widespread use during the summer months when inflammation causing insects (e.g. bees) and plants (e.g. poison ivy) are at their peak and a user is more likely to perspire freely or swim.
We have surprisingly found that one can prepare a highly substantive oil-in-water emulsion by incorporating therein a polyanhydride resin derived from octadecene-1 and maleic anhydride. The copolymers can be made by published methods such as those shown in U.S. Pat. No. 3,729,451.
The preferred polyanhydride copolymer is linear, has a molecular weight of 4,000-100,000, more preferably 40,000-60,000, and has the comonomers present in essentially a 1:2 to 2:1 molar ratio.
A most preferred copolymer is commercially available from Gulf Oil Chemicals Company under the tradename of PA-18. PA-18 is a solid, linear polyanhydride resin having a molecular weight of about 50,000, a specific gravity of 0.97, and a melting point range of 110.degree.-120.degree.. The name given to PA-18 in the Third Edition of the CTFA Cosmetic Ingredient Dictionary is Octadecene/Maleic Anhydride Copolymer. This preferred copolymer was generally recognized as an emulsion stabilization agent in water-in-oil emulsion systems in U.S. Pat. Nos. 3,846,546 and 3,860,700. It has not, however, heretofore been recognized as a substantivity improving agent in oil-in-water emulsion systems.
The preferred sunscreen compositions are anionic oil-in-water emulsions having a pH of about 6 to 10, preferably 7 to 9, and in which the polyanhydride copolymer is present at a concentration of about 0.01 to 5.0 percent, more preferably about 0.3 to 3.0 percent.
The preferred anionic emulsifiers in a sunscreen composition are the soaps formed from a fatty acid and an amine or alkali, e.g. stearic acid and triethanolamine; the reaction products of ethylene maleic anhydride copolymers and an amine or alkali, e.g. the EMA-91 resin sold by Monsanto and described in U.S. Pat. No. 3,821,363 with sodium hydroxide; and the reaction products of the polymers of acrylic acid cross-linked with a polyfunctional agent and an amine or alkali, e.g. carbomer 940 and triethanolamine.
The preferred medicament formulas containing an anti-inflammatory steroid are preferably nonionic oil-in-water compositions having a pH of 4 to 9, more preferably a pH of 4 to 6, and a polyanhydride copolymer concentration of 0.01 to 0.5 percent, more preferably 0.01 to 0.1 percent.
The sunscreen compositions of this invention all contain sunscreen agents which are effective in low concentrations and are generally of low solubility in water. Suitable sunscreen agents include the esters of para-aminobenzoic acid, and substituted para-aminobenzoic acid, e.g. octyl dimethyl PABA; certain esters of salicylic acid, e.g. homomenthyl salicate; certain benzophenone derivatives, e.g. benzophenone-3; and the esters of para-methoxycinnamic acid, e.g. octyl methoxycinnamate.
Various optional ingredients may be included in the formulation, such as perfumes; preservatives, e.g. parabens and imidazolidinyl urea; emollients, e.g, lanolin, cocoa butter; antiseptics; pigments; dyes; propellants; foaming agents; viscosity control agents; as well as any other class of materials whose presence may be cosmetically, medicinally or otherwise desirable.
The remainder of the composition would consist essentially of water which would generally be in a concentration of 40-95 percent, preferably 60-90 percent. It is, of course, understood that water is the external phase of an oil-in-water emulsion.